Abstract
Many of the continuous watershed models perform all their computations on a daily time step, yet they are often calibrated at an annual or monthly timeโscale that may not guarantee good simulation performance on a daily time step. The major objective of this paper is to evaluate the impact of the calibration timeโscale on model predictive ability. This study considered the Soil and Water Assessment Tool for the analyses, and it has been calibrated at two timeโscales, viz. monthly and daily for the War Eagle Creek watershed in the USA. The results demonstrate that the model's performance at the smaller timeโscale (such as daily) cannot be ensured by calibrating them at a larger timeโscale (such as monthly). It is observed that, even though the calibrated model possesses satisfactory โgoodness of fitโ statistics, the simulation residuals failed to confirm the assumption of their homoscedasticity and independence. The results imply that evaluation of models should be conducted considering their behavior in various aspects of simulation, such as predictive uncertainty, hydrograph characteristics, ability to preserve statistical properties of the historic flow series, etc. The study enlightens the scope for improving/developing effective autocalibration procedures at the daily time step for watershed models. Copyright ยฉ 2007 John Wiley & Sons, Ltd.